Abstract
A new species belonging to the terrestrial orchid genus Nervilia
is described from Kasi District, Vientiane Province, northern Laos.
Referable to the widespread and species-rich N. adolphi/punctata alliance
on account of its solitary flower, slender white and violet-marked labellum and
glabrous, angular leaf, N. kasiensis is morphologically most closely
allied to N. muratana of southern China and northern Vietnam. As in that
species, the flowering and leafing phases overlap, an unusual feature among
members of the genus. The new species can be distinguished from N. muratana by
its shorter inflorescence, its weakly spreading perianth with beige sepals, its
narrower labellum

with
a central pubescent strip on the epichile, its arched column, and by its
faintly tessellated leaf. A morphological description, line drawing and notes
on the species’ ecology and conservation status are presented.

Description

Nervilia
kasiensis S.W.Gale & Phaxaysombath, sp. nov. — Fig. 1, 2, 3

This
new species most closely resembles N. muratana S.W.Gale & S.K.Wu in the
outline of its labellum, in the shape of its leaf and in its non-hysteranthous growth
habit. However, N. kasiensis is distinguished from N. muratana by
its much shorter inflorescence (up to 4.3 cm in the former vs 6.5–10.0 cm in the
latter), its weakly spreading perianth (vs widely spreading in the latter) with
beige sepals (vs white in the latter), its narrower labellum (up to 6.4 mm wide
in the former vs 9–12 mm wide in the latter) with a central pubescent strip on
the epichile (vs shortly and sparsely hairy along the main veins in the
latter), its arched column (vs straight in the latter), and by its tessellated leaf
(vs uniformly dark green in the latter). — Type: Gale & PhaxaysombathHNL-KFBG 537b (holotype HNL, flowered in cultivation from Gale &
PhaxaysombathHNL-KFBG 537a), ex cult. Biotechnology & Ecology
Institute, Ministry of Science & Technology, Vientiane, Laos, 11 Mar. 2016;
Gale & Phaxaysombath HNL-KFBG 537a (paratype HNL, leaf), Khoun Lang
Cave, Kasi District, Vientiane Province, Laos, 29 Nov. 2015.

Etymology. Named after Kasi District,
northern Laos, in which this species was discovered.

Distribution — At
present known only from the type collection, which comes from fragmented primary
hill forest in northern Laos (Fig. 3). Its discovery in similar habitats
elsewhere in Laos as well as in neighbouring parts of Thailand and Vietnam
might be expected, although primary forest in the region continues to dwindle
rapidly.

Ecology — Nervilia
kasiensis is an understorey herb that grows in shade in deep organic soils
in moist, evergreen hill

forest
over limestone at c. 750 m altitude. The flowering shoot emerges in March,
while its tuber is still connected by a runner to the previous year’s leafy
shoot. The old leaf withers and a new leaf emerges from a separate runner after
anthesis. Multiple runners are produced both from nodes of the tuber itself and
from the subterranean stem of leafy shoots. The presence of a prominent rostellum
at the apex of the stigma (Fig. 2h) suggests that N. kasiensis is
outcrossing (cf. Gale 2007).

Conservation status —
Only a small population of fewer than ten emergent shoots was found at the type
locality. The availability of suitable habitat throughout the Khoun Lang Nature
Reserve offers hope that more plants occur nearby. However, on-going
destruction of primary moist broadleaved forest in northern Laos, as well as in
neighbouring parts of Indochina, indicates that this apparently restricted and
rare species is under considerable threat due to habitat loss. Pending surveys to
better gauge its distribution and abundance, N. kasiensis is for now
considered Data Deficient (DD; IUCN 2012). Note — On account of its glabrous,
angular leaf and the narrow, white and violet-marked labellum of its single
flower, N. kasiensis is immediately recognisable as a member of the N.
adolphi/punctata alliance. In addition to the characters noted in the
diagnosis that differentiate it from N. muratana, its closest morphological
ally, N. kasiensis is also distinguished by its relatively broader
tepals as compared to those of that species. In its non-spreading perianth, the
slightly concave base of its lip and the rounded hypochile auricles, N.
kasiensis is also similar to N. alishanensis T.C.Hsu, S.W.Chung
& C.M.Kuo, a species of Taiwan and Hainan Province in southeast China (Hsu
et al. 2012, Gale et al. 2015). However, overall dimensions of the leaf and
flower parts are otherwise markedly different, added to which N.
alishanensis lacks a functional rostellum and is reported to be
self-pollinating (Hsieh et al. 2013).